1. Field of the Invention
This invention relates to a management device to investigate the path states of a network, and to such a network system. More specifically, this invention relates to a management device or the like capable of immediate acquisition of path states of the network, and also capable of detecting path changes.
2. Description of the Related Art
In the prior art, the traceroute command is a command which ascertains path states in a network.
By starting the traceroute command, packets are transmitted to a destination address with a TTL (Time To Live: a time of expiration for the packet) increased in succession from “1”. The network nodes which are one hop, two hops, and so on counting from the terminal which has issued this command return packets indicating a timeout error, in accordance with the TTL value. By increasing the TTL in succession until the terminal at the destination address returns this packet, the path therebetween can be elucidated.
In another technology of the prior art, a format signal with a flag indicating path tracing is transmitted from a command-issuing terminal, and each node appends the receiving port address and the transmitting port address and transmits the format signal to the next node, so that the transmission path is traced from the connection of accumulated appended receiving port and transmitting port addresses (see for example Japanese Patent Laid-open No. 2000-244563).
Further, a method has been disclosed in which a dynamic packet filter is set along a path using transmitted filter setting packets, and the collection of data detected by the filter is used to trace actual packets in the network, to acquire path information (see for example Japanese Patent Laid-open No. 2005-312033).
However, the traceroute command must be issued by a network operator or user (hereafter “network operator or similar”) who operates a terminal himself. Originally, this command is a command issued by a network operator or similar after a network fault has been recognized by some method. Hence except in cases in which this command is issued at the time of occurrence of a fault, it is difficult to acquire the path state at the time of occurrence of a fault.
A script or other means may conceivably be used to automate, to a certain degree (for example, at fixed times), issuing of the traceroute command. However, similarly to the above problem, if the command is not issued at the time of occurrence of a fault, then it is difficult to acquire the path state at the time of occurrence of a fault.
Moreover, the traceroute command is a command limited to a particular set of circumstances, and does not compare the results preceding and following each packet issued by starting the command to ascertain path changes. Hence even when there is a path change, this command cannot notify the network operator or similar of this fact.
On the other hand, in the case of the methods disclosed in Japanese Patent Laid-open No. 2000-244563 and Japanese Patent Laid-open No. 2005-312033, the network operator or similar himself must operate the terminal in order to issue format signal or filter setting packet, and it is difficult to acquire the path state at the time of fault occurrence.